BEACH life can be tough when you have to cope with the dramatic changes of the tides. One species of marine snail seems to wear a heatproof coat to help it survive.
Turban snails, so-called because of the shape of their shells, are often found on rocky shorelines. Although most turban snails will eagerly feast on algae, turban snails of the Lunella coreensis species in Japan are coated in a mat of it. And they accumulate it as a vegetative jacket as they grow, until they are entirely covered at maturity.
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This type of algae also appears to only grow on the shells of this snail, although the reason why has been considered a mystery. Now a study suggests that the algae insulate the snails from sudden shifts in temperature as the tide recedes.
鈥淭he snails are regularly out of water and are exposed to sun at low tide,鈥� says Osamu Kagawa, a marine biology student at Tohoku University and lead author of the study. 鈥淭he difference in temperature between low tide and high tide is sometimes more than 20掳C.鈥�
Kagawa and his colleague Satoshi Chiba noticed that snails on boulders close to sandy areas of beach often lacked algal coats, and those inhabiting rockier areas almost always had them. The pair collected these coatless snails, and found that they were far less able to cope with heat than those blessed with a covering of algae.
Coatless snails left under heat lamps in the laboratory for 30 minutes 鈥� an attempt to mimic the heat of the sun on the beach after the tide has gone out 鈥� died at nearly double the rate of those with an algal fuzz (, ).
However, not everyone is convinced by the pair鈥檚 explanation. 鈥淭he rocky shore probably supports tidal pools that encourage algal growth,鈥� says David Marshall at the University of Brunei Darussalam. Snails living on the sandy beach can probably also find shade beneath the boulders there, helping them stay cooler. 鈥淭hus there is no advantage of supporting algal growth on the shell,鈥� he says.